Municipal Sewage Sludge Processing Method Effect on the Content of Polycyclic Aromatic Hydrocarbons

The aim of the study was to determine PAH content and the share of their individual groups in municipal sewage sludge at individual stages of their production and processing in a municipal wastewater treatment plant. Sludge samples were collected in three study cycles: autumn (November), winter (February) and spring (April) in 2017 and 2018. In each cycle the samples of initial sludge, excessive sludge after press, digestate sludge and digested dehydrated sludge were analyzed. Three samples were taken from each sludge for further analysis. The content of 16 PAH (naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)-pyrene, dibenzo(a,h)anthracene, benzo(g,h,i)perylene and indeno(1,2,3-c, d)pyrene) was determined in the samples in the Faculty Chemical Laboratory at Bialystok University of Technology. For this purpose, a gas chromatography method coupled to mass spectrometry using a GC/MS Agilent 7890B chromatograph was used. The results were given as single PAH compounds, which were then grouped by the number of aromatic rings. It was found that the total content of 16 PAHs depended on the type of sewage sludge and the highest one occurred in the initial sludge, and much lower in other sediments. The fermentation process, and more drainage of the fermentation sludge, reduced the content of 16 PAHs. The transformation processes had an influence on the hydrocarbon content in particular groups. The share of PAH groups depending on the number of rings in total 16 depended on the date of collection of studied sludges. In the studied sludges, a group of three and four-ring hydrocarbons dominated, and the least was two- and six-ring hydrocarbons. PAH content in all analyzed sludges did not exceed the norm for the total of 11 PAHs proposed by the European Commission for sludge used for agriculture.